Pasteurization is the heating of a consumable item at a temperature and for a time sufficient to kill various bacteria that might be in the product. Excess heating can ruin the product, hereinafter presumed to be a foodstuff, while overly rapid or irregular heating must be avoided in order to prevent the recipient, hereinafter referred to as a bottle, from breaking due to uneven thermal stresses.
This heat-treatment is typically carried out in a conveyor-type system where the filled and closed bottles are moved through four separate zones. In the first preheating zone the items are gently brought up to a temperature near the pasteurization temperature, the heating being relatively slow to avoid damaging the containers with uneven thermal stresses. In the second prepasteurization zone they are brought rapidly up to the pasteurization temperature. Then in the third pasteurization zone the items are maintained at the pasteurization temperature for the treatment time so as to kill any bacteria. In the fourth cooling zone the temperature of the pasteurized items is reduced to prevent the food from overcooking and to recover useful heat. In each zone the heat exchange is between the contained items and a liquid which is sprayed over them. To this end the process takes place in a so-called tunnel through which the bottles move on a conveyor underneath a sequence of transverse sprayer beams from which a liquid, normally water, at the desired treatment temperature is sprayed on the bottles. Since the transport speed is invariably constant as the belt extends the full length of the tunnel and never stops, the only way to control the length of the treatment time in a particular zone is by controlling how many sprayer beams are supplied with water at the particular treatment temperature needed.
Different foodstuffs need different treatment times and temperatures in each of the four different zones, and some foodstuffs require more or less than three different treatments. This means that a treatment plant must substantially reconfigure its treatment line whenever the product changes, something that frequently cannot be done to achieve ideal results so a tradeoff must be made between the ideal or desired treatments and what the equipment will permit.
The switchover from one treatment method to another in a prior-art machine therefore necessitates complicated reconnecting of the sprayer beams to the different-temperature liquid sources. To do so it is necessary to reconnect a group of hoses, manipulate a great many valves, or otherwise undertake some fairly time-consuming job. The equipment necessary in an apparatus to make it work in more than one pasteurization mode is thus fairly complex and expensive. Furthermore while it is possible, albeit taking some time and employing some expensive equipment, to switch the feeds on the sprayer beams, it is virtually impossible to segregate the liquids of the various zones so they can be recirculated; instead much heat is lost even if complex zone-to-zone recirculation systems are used.